Incandescent lamp.



S. O. HOFFMAN. INGANDBSGENT LAMP.

APPLICATION FILED MAR. 1;, 1912. 1,083,325. Patented Jan. 6, 1914.

2 SHEETS SHEEI SAMUEL O. HOFFMAN, OF SAN FRANCISCO, CALIFORNIA.

INCANDESCENT LAMP.

Original application filed July 17, 1911, Serial N0. 638,911.

To all -zo7u m it may concern:

Be it known that I, SA Mom. 0. l-lorrim v, a citizen of the United States, residing 1n the city and county of San Franclsco and State of California, have invented new and useful Improvements in Incandescent Lamps, of which the following is a specification.

This invention comprises a method for the production of light from an incandescent body, without the production of wasteful heat, and more generally, of producing radiation of particular wave lengths from a source emitting waves of the desired other wave lengths, with a consumption 0t energy equivalent to the desired radiation only. an l not to the total radiation of the source.

The drawings illustrate suitable means for practisingthe invention; Figure 1 being a side elevation in partial section of a complete lamp embracing the invention. Fig. 2 is a transverse section of a portlon of the inner bulb of Fig. 1, drawn on a greatly enlarged scale. Fig. 3 is a modification. showing a simple form of the invention in which film of silver is applied to the inner sin-tare of a'lamp bulb.

Lie-ht consists of waves in the ether of certain lengths, capable of afiectino' the retina. Waves of greater length, called 1nfra-red waves are non-luminous. Both the luminous and infra-red waves upon absorption by a body are converted into heat. Aside from their physiological effects, the only diflerence between the luminous and infra-red waves is the longer wave length of the latter.

Practically all of the present systems of lightingdepend upon the radiation of incandescent bodies. The radiation of such a body consists of waves of all lengths, only a small portion of which are luminous. most of the energy being: in the longer non-luminous ini'rwred waves. The Wave length carryinq the maximum energy decreases as the temperature is raised, according to the Wien displacement law, and the higher the temperature the larger the proportion of luminous radiation present. At the highest possible operating temperature. only about 17 5% of the radiation is of useful wavelength (luminous) the balance being infrared waves and non-luminous, so called heat waves.

Specification of Letters Patent.

Thus at least 95% of the energy.

Patented Jan. 6, 1914. Divided and this application filed March 19,

Serial No. 684,749.

used to kee the body incandescent is radiated as long non-luminous Waves (heat) and so wasted.

My invention consists simply in separat ing the radiation of the incandescent body into the luminous and non-luminous portions; and small luminous percentage being allowedto radiate freely,.while the non-luminouswaves, representing most of the energy, are directed back to the incandescent body and used regeneratively, none being allowed to escape. Thus there is no loss of heat except that representing the small proportion of in iinous radiation-produced, and the energy required to keep the body at the necessary temperature is equivalent to the light produced, and not to the total radiation at that temperature, resulting in an enormous increase in eiiiciency. Of course the simplest way of accomplishing this is to use a substance waves and reflects the non-luminous. I have found that a film of metallic silver, thin enough to be transparent, reflects a large proportion of the infra-red waves. Fig. 3 shows a lamp making use of this fact. A filament C is placed as nearly as possible along the axis of the cylindrical tube A. on the inside of which is deposited a thin film of silver. The lamp is otherwise similar to the ordinary incandescent electric lamp. The combined radiation from the filament strikes the inner metallic film normally, the infra-red waves are reflected back to the filament. while the light passes through.

While I have only shown two methods of practising my invention. it is possible to make use of any means whatsoever by which the luminous waves can be separated from the non-luminous; the essence of my invention being the fact that the non-luminous radiation is directed back to the source without loss and used regeneratively. For instance with respect to the first method described. there are a large number of substances known to physicists which have the property of selective reflection. I have mentioned silver simply because I have actually and successfully tried it.

Another method of producing the invention is as follows: Instead of the film of silver. a glass bulb B shown in section in Fig. 2, is placed inside the tube A. This bulb has prismatic surfaces formed upon it, the efl'ect of which is to transmit the light and which transmits the luminous reilect the infra-red waves. This bulb is made as thin as practicable. to prevent. loss by abscrpt ion. its action depends upon the following principles: A radiant beam passing obliquely from one medium to another is bent or refracted, to or from the normal to the oblique surface, depending upon whether the beam is entering a denser or rarer medium. The amount of refraction varies with the wave-length of the incident radiation, with the angle of incidence and with the nature of the medium. For any given medium and wave length, the ratio of the sincs of the angles of incidence and refraction is a constant, known as the refractive index. For the same medium, the refractive index varies with the wave length of the incident radiation, being greater for luminous than infra-red waves, etc. If a radiant beam endeavors to pass from a dense to a rarer medium, at an angle to the normal greater than a certain critical angle, it will not succeed in passing out, but will be totally reflected; in fact this arrangement makes the most perfect reflector known. Now this critical angle of total reflection is equal to the angle whose sine is the reciprocal of the refractive index, and therefore, is less for waves'of short than of long length and less for luminous than for infra-red waves. In a particular glass that I experimented with. the refractive index for red light, the light of longest wave length, was 1.528, and for the maximum infra-red 1.- t96. Therefore the critical angle for red light (sine of critical angle reciprocal of refractive index) is 40 53, and for the maximum infra-red wave length about 4 It is apparent, therefore, that if a beam containing luminous and infra-red waves should seek to leave the glass at an angle to the normal of about 41, the red and therefore all the luminous waves would be totally reflected, while the infra-red would pass out.

Referring to Fig. 2, which is a greatly enlarged section of a portion of the inner bulb B, the angles are as shown. Of course the necessary angles would depend upon the refractive index of the particular glass used, in this case the values are those given in the preceding paragraph. A radiant beam K from the filament containing luminous and infra-red waves enters the glass normally and strikes the surface as at M at an angle of 41: as this is greater than the critical angle for the luminous waves, they will be totally reflected along the path M I, again reflected at P and finally passing out normally along the path P H, but the angle 41,

is less than the critical angle for the infrared waves, therefore, they will pass out. it ing refracted along M O, striking the surface 0 of the right angle prism at an angle of 45 and being reflected along 0 R, again reflected at R, along R S, entering the glass at S and passing out normally, as at T, thence hack to the filament. It is thus seen that no radiant energy can escape from the filament except in the form of luminous waves, the infra-red waves, which carry more than 95% of the energy being continually reflected back, and used regeneratively. In the arrangement shown for practical reasons, there will be a small waste space as at E. To prevent loss, this space is closed with right angle prisms which refleet back both light and infra-red radiation, as the beam Y, lV, X, Z. If the surface M were so constructed that the beam should strike it at say 415, a large portion of the red rays would be reflected back along with the infra-red and thus a source (filament) giving out a light rich in red, could be made to give a pure white light. This also is of importance as allowing incandescentlamps to be run below voltage this giving a very long life. \Vhile the lamp I have illustrated is an incandescent electric lamp, it is of course a simple matter to adapt the principle of the invention to any lamp using an incandescent body or bodies.

The word regenerative in this application and in the claims, is employed in the sense of. being used again or repeatedly without appreciable or apparent loss. The term selective reflector used in this application and in the claims, means any sort of a reflector or reflecting surface or object which has the capacity of separating the luminous radiation from the non-luminous, allowing one class of radiation to radiate and reflecting the radiation of the other class to a source of radiation.

The essence of this invention is the keeping of a radiant medium or source, incandescent; allowing the escape of only radiation of a certain definite character with no apparent or appreciable loss of radiation of any other or different character; the nudesired radiation, or radiation of undesired wave length being conserved and repeatedly returned to the source where it is absorbed and acts to kep the body or source incandescent with a very small amount of additional extraneous energy; the extraneous energy being only sufficient to make up for the escape of desired radiant ener y. That is what is meant by using certain radiation regeneratively.

This application is a division of my original application filed July 17, 1911, Serial No. 638,911.

Having thus described my invention, what I claim and desire to secure by Letters Patent is 1. The combination with a source of incandescent radiation, of a selective reflector surrounding and inclosing the source and characterized by this that it intercepts and returns to the source the non-luminous radisource of radiation and formed to permitation and permits the luminous radiation to pass therethrough and radiate freely.

2. A lamp embodying a source of radiation of waves of varying length, a selective reflector surrounding and inclosing the completely surrounding said source and characterized by this that itselectively intercepts and returns to the source the. nonluminous radiation for use regeneratively and permits the luminous radiations to pass freely through the same.

4. A lamp embodying a source of radiation of waves of various lengths, and a selective reflector embodying refracting surfaces for separating the waves of different length and allowing luminous radiation to pass; said reflector having reflecting surfaces disposed in the path of'the non-luminous radiation and cooperating with means for converting the non-luminous radiation into luminous radiation.

5. An incandescent lamp comprising, in combination, an incandescent source and a reflective inclosure surrounding and completely enveloping the source, whereby all radiation escaping from the lamp mustpass therethrough, said reflective inclosure being characterized by this, that it selectively intercepts and returns to the source the nonluminous radiation for use regeneratively and permits the luminous radiation to pass freely through the same.

6. A lamp consisting in combination of an incandescent source and a globe therefor having prismatic surfaces so arranged as to separate the desired radiation from the undesired, and to reflect the undesired radiation back to the source.

7. A lamp consisting in combination of an incandescent source and a bulb therefor,

said bulb constructed and arranged with re-.

spect to the source, as to provide a series of prismatic surfaces with the critical angle of total reflection such that the desired radiation is separated from the undesired and the. latter reflected back to the source.

8. 'A lamp consisting in combination of an incandescent source, a reflector, said reflector constructed and arranged with respect to the source in accordance with the formula that the critical angle is equal to the re ciprocal of the refractive index so that the desired wave lengths of radiation are allowed to radiate freely while the undesired are reflected back to the source.

9. A lamp consisting in combination .of

an incandescent source and a globe therefor having prismatic surfaces so arranged as to separate the luminous radiation from the infra-red, and to reflect the infra-red radiation back to the source.

10. A lamp consisting in combination of an incandescent source and a bulb therefor,

said bulb constructed and arranged with re spect to the source, as to provide a series of prismatic surfaces with the critical angle of total reflect-ion such that the luminous radiation is separated from the infra-red and the latter reflected back to the source.

11. A lamp consisting in combination of an incandescent source, a reflector, said reflector constructed and arranged with respect to the source in accordance with the formula thatthe critical angle is equal to the reciprocal of the refractive index so that the luminous wave lengths of radiation are allowed to radiate freely while the infra-red are reflected back to the source.

In testimony whereof I have hereunto set my hand in the presence of two subscribing Witnesses JAMES Mason,

M. COL INS. 

